Synthetic and biosynthetic studies of porphyrins. Part 9. Synthesis of isocoproporphyrin, dehydroisocoproporphyrin, and de-ethylisocoproporphyrin

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Abstract
The title compounds, which were excreted by patients suffering from porphyria cutanea tarda or rats poisoned with hexachlorobenzene have been synthesized by the b-oxobilane route. Isocoproporphyrin tetramethyl ester (7a) was prepared from pyrromethanes corresponding to rings DA and BC of the macrocycle, and the de-ethyl analogue (7b) was prepared in a similar fashion; acetylation of the latter followed by reduction and dehydration then afforded dehydroisocoproporphyrin tetramethyl ester (7d). Minor by-products arising in the syntheses have been shown to arise by rearrangement of the BC pyrromethane.